Download - Amphibian Use of Chehalis River Floodplain Wetlands

Amphibian Use of Chehalis River Floodplain WetlandsAuthor(s): Julie A. Henning and Greg SchiratoSource: Northwestern Naturalist, Vol. 87, No. 3 (Winter, 2006), pp. 209-214Published by: Society for Northwestern Vertebrate BiologyStable URL: http://www.jstor.org/stable/4501964 .

Accessed: 12/06/2014 23:18

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Society for Northwestern Vertebrate Biology is collaborating with JSTOR to digitize, preserve and extendaccess to Northwestern Naturalist.

http://www.jstor.org

This content downloaded from 188.72.126.41 on Thu, 12 Jun 2014 23:18:42 PMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=snwvb

http://www.jstor.org/stable/4501964?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


NORTHWESTERN NATURALIST 87:209-214 WINTER 2006

AMPHIBIAN USE OF CHEHALIS RIVER FLOODPLAIN WETLANDS

JULIE A HENNING1

Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331- 3803; [email protected]

GREG SCHIRATO

Washington Department of Fish and Wildlife, 48 Devonshire Road, Montesano, Washington 98563

ABSTRACT-The use of isolated emergent wetlands by amphibians has been well documented.

However, amphibian habitats such as emergent wetlands in floodplains may differ from isolated wetlands because of their high disturbance (water fluctuation) related to riverine flooding, presence of fish species, and increased connectivity among aquatic habitats. We compared the am-

phibian assemblages at 6 freshwater wetland habitats in the Chehalis River floodplain and ex- amined the effect of wetland restoration on amphibians. We sampled 6 wetlands during the

breeding season in 2003 and 2004 and captured over 15,000 adults, tadpoles, and larvae from 6 species. The red-legged frog (Rana aurora) was the most abundant species captured. The rough skinned newt (Taricha granulose) was the only amphibian captured at all sampled sites. Although it is more desirable to prevent wetland degradation from occurring, restored and enhanced wetlands in floodplains do provide breeding habitat for amphibians. Amphibian species captured in reference wetlands were also captured in restored wetlands. Water control structures, which were used to facilitate wetland restoration, did not seem to influence utilization by amphibians; however, hydroperiod seemed to affect amphibian abundances. Wetlands with intermediate hydroperiods had the highest amphibian abundance compared to wetlands with temporary or

permanent water. Fish were captured in all wetlands, and those with the greatest abundance of native non-game fishes had the highest abundance of amphibians. Our results suggest that

emergent wetlands in floodplains are dynamic habitats that can offer breeding opportunities, but microhabitat suitability needs to be considered when managing amphibian habitats.

Key words: red-legged frog, Rana aurora, Pacific treefrog, Pseudacris regilla, bullfrog, Rana catesbeiana, rough-skinned newt, Taricha granulosa, northwestern salamander, Ambystoma gracile, long-toed salamander, Ambystoma macrodactylum, amphibians, wetlands, floodplains, restora-

tion, habitat, Chehalis River, Washington

Freshwater emergent wetlands are common features of large river-floodplain systems. Flood disturbances enhance the productivity of these wetlands, increase wetland water fluctuation, and allow riverine fish to access flood-

plain habitats (Bayley 1991, 1995). Many am-

phibians use wetlands for mating, oviposition, and larval growth and development (Semlitsch and others 1996). Studies of amphibian use of

river-floodplain wetlands in the Pacific North-

west, however, are infrequent. Most of the published work to date has dealt with amphibian use of inland wetlands and isolated palustrine

habitats (such as Richter and Azous 1995). These habitats differ from isolated wetlands because river-floodplain wetlands have higher levels of disturbance (water fluctuation) related to riverine flooding, have increased connectiv-

ity among aquatic habitats, and often contain fish. Water level fluctuations or the presence of exotic fish have been shown to decrease am-

phibian richness (Richter and Azous 1999; Pearl and others 2005).

Freshwater wetland restoration projects in

floodplain environments are designed and

managed for emergent vegetation, fishes, and waterfowl. Amphibians are rarely a management focus. Consequently, our goal for this

study was to describe the amphibian assem- 1 Present Address: Washington Department of Fish and Wildlife, 1182 Spencer Road, Toledo, Washington 98591.

209



210 NORTHWESTERN NATURALIST 87(3)

blages in floodplain wetland habitats of the Chehalis River Valley in southwestern Wash-

ington. Our specific study objectives were to

quantify and compare amphibian use across the floodplain at 6 study sites and to determine the effect of wetland restoration on amphibians. Subsequently, we evaluated the potential influence of hydroperiod on amphibian use at the study sites.

METHODS AND STUDY AREA

The study was conducted in Grays Harbor

County in an agricultural floodplain landscape of the Chehalis River. The Chehalis River Basin has a drainage area of approximately 6900 km2 and is the 3rd largest river basin in the State of

Washington. The study sites were located in the lower Chehalis Basin (below river kilometer 60) where the river is unconstrained and sinuously moves through the floodplain in the broad flat

valley floor. The basin was chosen for sampling because of its large size and relatively intact and minimally degraded floodplain.

Six sites were studied: 4 emergent wetlands and 2 oxbow wetlands in the Chehalis River

floodplain between river kilometer 27 and 60. Two of the 4 emergent wetlands were restored sites with water control structures (R1 and R2), and 2 were reference wetlands (N1 and N2). The reference wetlands were naturally occur-

ring and had not been impacted by ditching. The oxbow habitat site, 01, was a remnant oxbow with a beaver dam that contained permanent water. The other oxbow habitat site, 02, was a seasonal side-channel wetland off the river's main-channel. All study sites contained fish species (see Henning and others 2006).

Restored wetlands R1 and R2 contained rennie and salzer clays (USDA SCS 1986) and were drained as part of a local drainage district project to facilitate farming. Wetland enhance- ments in 1997-98 involved blocking drainage ditches by constructing water control structures and levees. The water control structures enhanced wetland hydrology by retaining water, and levees kept water within the project area to avoid flooding adjacent lands. Water ac- cumulation provided conditions for a diversity of emergent vegetation and reduced nonnative reed canarygrass (Phalaris arundinacea). Winter water depths were similar at the restored sites (1 to 1.5 m). R1 during the summer desiccated to 0.5 ha, but R2 retained about 1 ha of standing

water. Dense, monotypic stands of invasive reed canarygrass dominated the vegetation at both wetlands before enhancement. After restoration at R1, native emergent vegetation increased and included narrowleaf bur-reed

(Sparganium angustifolium), swamp smartweed

(Polygonum hydropiperoides), waterpurslane (Di- diplis diandria), mannagrass (Glyceria sp.), slough sedge (Carex obnupta), and yellow pond- lily (Nuphar lutea). The R2 wetland was drawn down to allow vegetation to germinate during the growing season. Dominant vegetation was reed canarygrass, spotted ladysthumb (Polyg- onum persicaria), narrowleaf bur-reed, marsh cudweed (Gnaphalium uliginosum), slough sedge, and bentgrass (Agrostis sp.).

The N1 and N2 reference sites lacked water control structures and were chosen based on their proximity and similarity to the restored wetlands, R1 and R2, respectively. The reference wetlands had not been ditched or drained and contained rennie and salzer clays. Re- stored and reference sites connected to common water bodies and exhibited similar hydro- logical patterns and river flows. The wetlands had free-flowing hydrologic connections to the river's mainstem during periods of peak dis-

charge. However, the reference wetlands did not have surface water outlets, and surface water disappeared by May at N1 and in July at N2.

Emergent vegetation colonized the wetlands

during desiccation. N1 was dominated by reed

canarygrass. N2 vegetation consisted of reed

canarygrass, common spikerush (Eleocharis pal- ustris), narrowleaf bur-reed, sedge (Carex sp.), and waterpurslane.

The oxbow habitats (01 and 02) did not contain water control structures or emergent wetland characteristics. The sites had free-flowing hydrologic connection to the river during most of the sampling season. The 01 study site was a remnant channel with permanent water and connected upstream to the same drainage as N1 and R1. Water permanence in the oxbow was retained by spring inputs and a beaver dam. 01 also had steep channel slopes, minimal emergent vegetation, and an abundance of

large wood. Dominant vegetation was yellow pond-lily and largeleaf pondweed (Potamogeton amplifolius), and the site was bordered by reed canarygrass, willow (Salix sp.), Sitka spruce (Picea sitchensis), and Himalayan blackberry (Rubus discolor). The 02 study site was a sea-



WINTER 2006 HENNING AND SCHIRATO: AMPHIBIANS IN FLOODPLAINS 211

sonal channel directly connected to the river in winter. Site depth and discharge were depen- dent on river stage. 02 desiccated by mid-May and reed canarygrass dominated the oxbow.

Relative amphibian abundance was evaluated using fyke nets from January to May 2003. Each net consisted of a 5-ringed steel hoop net with 2 trapping throats that were 4.5 m long, 1.2 m wide, and covered with 4.76-mm mesh

netting. Nets were set perpendicular to the shoreline along the wetland perimeter and sep- arated to maintain independence during each 24-h sampling period. The number of nets per site was proportional to the wetland surface area and nets were set to not exceed a maxi- mum density of 1 net/ha in each wetland. Abundance was expressed as catch-per-unit-effort (CPUE), which was defined as the number of amphibians captured in a fyke net over a period of 24 h. Catch-per-unit-effort estimates for each month of sampling were combined to ob- tain an average monthly CPUE for each study site.

One-way emigrant traps were installed downstream of study sites that contained a defined outlet (R1, R2, 01, and 02) to examine

amphibian abundance and emigration. The

traps were operated from 4 March to 5 June 2003. Abundances at R1 and R2 were reexam- ined using emigrant traps from 7 January to 4

June 2004. Each emigrant trap consisted of a

0.6-m X 1.2-m holding box attached to wing nets that channeled amphibians into the box for identification and counting. The traps operated continuously except during floods when trapping became inefficient or when the site desiccated and the trap became dry.

RESULTS

Amphibians utilized all of the river-flood-

plain wetlands studied, although abundances were highest at the restored sites and at the N2 reference site (Fig. 1). Fyke nets and emigrant traps captured 13,201 individuals in 2003 and

emigrant traps captured 2198 individuals in 2004. Four amphibian families representing 3

frog and 3 salamander species were captured at the 6 study sites.

Species abundances of amphibians varied

among the study sites (Fig. 1). Red-legged frog (Rana aurora) tadpole abundances were significantly higher in N2 than in N1, 01, and 02

(Kruskal-Wallis single factor analysis of vari-

5- C 4

3- E

2-Z

N2 Ri St2 /V 12 0 02 Site

FIGURE 1. Catch-per-unit-effort (CPUE, number/ net/24-h trapping period) of amphibian species captured at 2 restored wetlands (R1 and R2), 2 reference wetlands (N1 and N2), and 2 oxbow habitats (01 and

02). RC = bullfrog, RA = red-legged frog, AG = northwestern salamander, TG = rough-skinned newt. Adult and tadpole or larval life stages were combined for all species except RA for which only the adult CPUE's are shown. RA tadpole CPUE's (N2 = 605, R1 = 141, R2 = 120, and N1, 01, and 02 <1) were not included because of the scale of the figure.

ance by ranks: X2 = 31.85, df = 5, P = 0.00; non-

parametric multiple comparisons with unequal sample sizes (Zar 1996), Qo.o5,5 = 2.94, P <

0.05)(see Fig. 1 caption). Rough-skinned newt

(Taricha granulosa) larvae and adults were captured at all study sites, but abundances were

significantly higher at R1 compared to the other sites with the exception of N2 (Kruskal-Wal- lis single factor analysis of variance by ranks:

X2 - 58.02, df = 5, P = 0.00; nonparametric

multiple comparisons with unequal sample sizes, Qo.o5,5 = 2.94, P < 0.05). Northwestern salamander (Ambystoma gracile) larval and adult abundances were higher in R1, R2, N2, and 02 compared with N1 and 01 where no northwestern salamanders were captured. Nonnative bullfrog (R. catesbeiana) adults and

tadpoles were most abundant at R2, but a few were captured at R1 and 01. No bullfrogs were

captured at N1, N2, and 02. Long-toed salamander (A. macrodactylum) adults were captured at all sites except 01, and CPUE ranged from 0 to 1.1. The highest long-toed salamander abundances were recorded at N1 and N2

(17 and 10 individuals, respectively), 6 individuals were captured at R1, 2 at R2, and 7 at 02.

Long-toed salamander larvae were not captured at any of the study sites. Thirteen Pacific

treefrog (Pseudacris regilla) adults were cap-




TABLE 1. The number of individuals per species captured in 1-way emigrant traps at oxbow habitats (01 and 02) and restored wetlands (R1 and R2) in the Chehalis River floodplain, Washington, during 2003 and 2004. Note: 02 had flooding and was the earliest site to desiccate, reducing trap nights in 2003.

01 02 R1 R2 R1 R2 Species 2003 2003 2003 2003 2004 2004

Ambystoma gracile larvae and adults 0 0 62 10 10 52 Ambystoma macrodactylum adults 0 0 1 0 3 3 Taricha granulosa larvae and adults 0 1 243 4 281 72 Rana aurora adults 0 2 245 22 21 52 Rana aurora tadpoles 0 0 1414 1635 743 58 Pseudacris regilla adults 0 0 4 11 1 0 Rana catesbeiana adults 1 0 1 21 4 72 Rana catesbeiana tadpoles 2 1 7 640 9 621 Total amphibians 3 4 1977 2343 1072 930 Total trap nights 32 16 34 35 28 32 Number/trap night 0.09 0.25 58.1 66.9 38.3 29.1

tured at the reference sites (2 at N1; 10 at N2) and at oxbow habitat 02 (1 frog).

Species richness ranged from 2 to 5 species per study site and the rough-skinned newt was the only species captured at all sites (Fig. 1). Restored and reference wetlands had similar

species richness (4 to 5 species). 02 had a species richness of 5, and 01 had a species richness of 2.

The 1-way emigrant trap results showed that a considerably higher number of amphibians emigrated from the restored sites than from the oxbow sites. Also, the rate of amphibian emi-

gration (measured as the number of individuals captured per trap night) from the restored sites was higher in 2003 than in 2004 (Table 1).

Differences in hydroperiod were identified

among the study sites. The restored sites had intermediate hydroperiods with >7 mo of inundation. Although the restored sites were drawn down in the spring, they each contained a small (<1 ha) permanent pond throughout the year. Reference site N2 had an intermediate

hydroperiod similar to the restored sites and

completely desiccated by August. Reference site N1 and oxbow site 02 had short hydroperiods with <5 mo of inundation and were desiccated before June. Oxbow site 01 was per- manently saturated and had the longest hydroperiod compared with the other study sites.

DIscUSSION

All amphibian species, except Pacific tree-

frog, captured at the reference sites were captured at the restored sites. High amphibian abundances at the restored sites suggest that these habitats were successful in providing

breeding habitat for most amphibians. Am-

phibians inhabiting wetlands in the floodplain have substantial dispersal potential because the aquatic habitats are not isolated, unlike ur- ban habitats where there are strong dispersal barriers (such as roads) and amphibian immi-

gration and dispersal may be more difficult

(Lehtinen and others 1999). The reference site N2 had the highest abundances of red-legged frog adults and tadpoles compared to the other sites (Fig. 1). This wetland was the only site that had an intermediate hydroperiod and was

completely desiccated in late summer. These

hydrologic conditions allowed emergent vegetation to germinate and probably kept non-native bullfrogs and fishes from inhabiting the site. Also, red-legged frogs successfully bred at all sites except N1, which had the shortest hydroperiod, and 01, which had the longest hydroperiod of all the sites. These results suggest that amphibian abundances were higher at seasonal wetlands with intermediate hydroperiods (R1, R2, and N2) than at seasonal wetlands with shorter hydroperiods (N1 and 02) because wetlands with intermediate hydroperiods remain inundated long enough to allow larvae to metamorphose. Permanent inundation such as at site 01 often contributes to the

presence of predatory fish and minimal emer-

gent vegetation. Lack of emergent vegetation decreases habitat for amphibian egg deposition (Nussbaum and others 1983) and affects invertebrate communities (Richter and others 1991). Wetlands that have water drawdowns provide conditions suitable for emergent vegetation to

germinate. In addition, areas with diverse



WINTER 2006 HENNING AND SCHIRATO: AMPHIBIANS IN FLOODPLAINS 213

emergent vegetation have high invertebrate abundance and diversity (Fredrickson and Reid 1988). This is important because amphibian abundance and species richness have been

positively correlated with invertebrate abundance and richness (Babbitt and others 2003).

Species present in river-floodplain systems must be adapted to flooding disturbance caused when riverbanks are overtopped and the river and floodplain connect. In the Che- halis River floodplain, heavy rain events can

trigger riverine flooding causing the river to in- undate the river's floodplain. This disturbance occurs across the floodplain 2 to 3 times during the winter and spring months in most years. This study, although the sample size was small, showed that amphibians utilized floodplain wetlands prone to varying levels of water fluctuation. In contrast, Richter and Azous (1995) found that species richness of amphibians was

negatively correlated with high water fluctuations. This correlation, however, was deter- mined for an urbanized watershed where im-

pervious surfaces tend to increase water fluctuations to levels at which amphibians may not be adapted.

Water fluctuations due to flooding of flood-

plain habitats also increase the presence of fish in seasonal wetlands. Although fish were present at all of the study sites, they did not appear to greatly affect the amphibian assemblages. For instance, sites that had the highest amphibian abundances (R1, R2, and N2) were also the sites with the highest native fish abundances

(threespine stickleback [Gasterosteus aculeatus] and State Sensitive Species, Olympic mudmin- now [Novumbra hubbsi]) (Henning and others 2006). Amphibians likely coevolved with native fish in floodplain landscapes, and so the fish

may have minimal impact on amphibians. However, study sites that had permanent water and an abundance of bullfrogs and exotic fishes had low amphibian abundance. Pearl and others (2005) found similar results in the Willam- ette Valley of Oregon, where most native am-

phibians had negative associations with the

presence of non-native fish. Seasonal wetland habitats that are important

for amphibian populations may be the most impacted by agriculture, especially in floodplain landscapes. Although these habitats have been ditched and drained, they can be enhanced with water control structures that increase wet-

land surface area and alter hydroperiod, cre-

ating conditions suitable for amphibians and colonization by emergent vegetation. Although it is more desirable to prevent wetland degradation from occurring, restored and enhanced

floodplain wetlands can provide habitat for successful amphibian breeding. However, our data suggest that not all floodplain aquatic habitats are important for amphibians; therefore, considering the microhabitat suitability is im-

perative to the success of conserving seasonal wetlands for amphibian populations.

ACKNOWLEDGMENTS

This study was supported by the US Environmen- tal Protection Agency, Aquatic Resources Unit, Re- gion 10, grant number CD-97024901-1, and the Washington Department of Fish and Wildlife. We thank 2 anonymous reviewers for providing com- ments that greatly improved the manuscript.

LITERATURE CITED

BABBITT KJ, BABER MJ, TARR TL. 2003. Patterns of larval amphibian distribution along a wetland hydroperiod gradient. Canadian Journal of Zoology 81:1539-1552.

BAYLEY PB. 1991. The flood pulse advantage and the restoration of river-floodplain systems. Regulat- ed rivers: Research and Management 6:75-86.

BAYLEY PB. 1995. Understanding large river-floodplain ecosystems. Bioscience 45:153-158.

FREDRICKSON LH, REID FA. 1988. Invertebrate re-

sponse to wetland management. Waterfowl management handbook. Washington, DC: US Fish and Wildlife Service. Fish and Wildlife Leaflet 13.3.1. p 1-6.

HENNING JA, GRESSWELL RE, FLEMING IA. 2006. Ju- venile salmonid use of freshwater emergent wetlands in the floodplain and its implications for conservation management. North American Jour- nal of Fisheries Management 26:367-376.

LEHTINEN RM, GALATOWITSCH SA, TESTER JR. 1999.

The effects of habitat loss and fragmentation on wetland amphibian assemblages. Wetlands 19:1- 12.

NUSSBAUM RA, BRODIE ED JR., STORM RM. 1983. Am-

phibians and reptiles of the Pacific Northwest. Moscow, ID: University of Idaho Press. 332 p.

PEARL CA, ADAMS MJ, LEUTHOLD N, BURY, RB. 2005.

Amphibian occurrence and aquatic invaders in a changing landscape: implications for wetland mitigation in the Willamette Valley, Oregon, USA. Wetlands 25:76-88.

RICHTER KO, Azous AL. 1995. Amphibian occurrence and wetland characteristics in the Puget Sound Basin. Wetlands 15:305-312.




RICHTER, KO, Azous A, COOKE SS, WISSEMAN RW, HORNER RR. 1991. Effects of stormwater runoff on wetland zoology and wetlands soils charac- terization and analysis. Olympia, WA: Washing- ton State Department of Ecology. Report Project G0091019. p 144.

SEMLITSCH, RD, SCOTT DE, PECHMANN JHK, GIBBONS

JW. 1996. Structure and dynamics of an amphibian community: evidence from a 16-year study of a natural pond. In: Cody ML, Smallwood JA, ed- itors. Long-term studies of vertebrate assemblages. San Diego, CA: Academic Press. p 217-248.

[USDA SCS] UNITED STATES DEPARTMENT OF AGRI-

CULTURE, SOIL CONSERVATION SERVICE. 1986. Soil

Survey of Grays Harbor Area, Pacific County, and Wahkiakum County, Washington.

ZAR JH. 1996. Biostatistical analysis., 3rd ed. Upper Saddle River, NJ: Prentice-Hall, Inc. Various pag- ings.

Submitted 18 May 2005, accepted 1 February 2006.

Corresponding Editor: RL Hoffman.



Download - Amphibian Use of Chehalis River Floodplain Wetlands

Top Related